Hyundai Porter | Cold start problem

Many diesel vehicles manufactured after the year 2000 are equipped with a common rail diesel system. Using the wrong fuel, mistaken maintenance, and engine overheating can force a diesel car into a garage for investigation and repair. This car had a cold start problem, where the engine ran poorly and white smoke was apparent. The previous engineer had changed injectors and the actual engine head, however the problem still occurred.

We checked the compression using the scan tool, however in this case the scan tool showed compression as normal without any faults.

Figure 1: Cylinder balance test when warm

First we did a basic compression test using PicoDiagnostics, and found there was one cylinder suffering from low compression. Finally we had found that this was due to a bent con rod. Using the scan tool had shown compression as normal and the engineer trusted it. This resulted in wasting time and money changing injectors three times and the engine head. The final conclusion is far simpler when considering his effort.

Figure 2: Compression test result using PicoDiagnostics

Of course, there are some engineers who swap adapted injectors to normal injectors so that they can distinguish if this is an injector problem or mechanical problem, however, these engineers must have a scan tool which has a injector adaption function for a specific vehicle. In addition to this if accessing the injectors is difficult, without knowing for sure if this was a problem or not, the engineer is wasting a lot of time. The customer wants to know the exact problem and receive a quick repair. PicoScope did a great job in identifying the problem, and saved our engineer time in the process.

Comments

Hello, thank you very much for this article. Very informative. Was wondering if the engine was at full operating temp for both cylinder balance tests? It fascinates me that the Scanner failed completely to pick this up when it is doing essentially the same thing as the Pico scope e.g. using small battery voltage fluctuations to determine a cylinder than won’t slow rotation as much as the others. Is it possibly due to pico scope having a higher sampling rate than scan tool or something?

Phil JJune 23 2012

David . I agree a proper mechanical compression test is preferable but knowing how difficult and troublesome it is to remove heater plugs from some diesels it is a lot easier to use the pico with just a connection to the vehicles battery.
At least to make a preliminary diagnosis.

david millnJune 05 2012

although the pico is a great tool. good old fashioned diagnostics still works. I’d rather use a proper compression tester with jobs like this, and would of been one of my first tests after diagnotics on a sympton like this.

Andy from Cape Auto DiagnosticsJune 03 2012

Hello from Cape Town, I used offten cylinder balance test but I found that the results spread a lot. One test shows ok, the next can show 1 cylinder fails. I do it 10 times with same engine to get a avarage. But can still be 50/50 results. The problem is that the accurancy of the test is influenced by a lot of conditions. Therefore I would do than a 2nd or 3rd different test like absolute comnpression, or cranking amps to confirm. Its more effort but I would not strip the engine based on Cyl Balance test only.
Regards Andy

Allan PietersenJune 03 2012

Hi,
I still maintain Picoscope diagnostic equipment is still the BEST.

g meeksJune 01 2012

pico scope is one of the best

Tom DentonJune 01 2012

A great reminder of how important the most basic diagnostic tests are. And how easy to do on the PicoScope. Far too many places bolt on new parts to see if that will fix the problem! Keep these articles coming.

SurajMay 31 2012

Could a more detailed description be provided
Which Scanner used for the Cylinder balance?
Did the Tech, How did he check with the picoscope?
Why did the Scanner show 100 for Cylinder balance?

RobskiMay 31 2012

What did the injection corrections show when cold ?

NIGEL VERA JACKSONMay 31 2012

in my case if i was to use my Verus scope could have done a compression test using my amp probe connected to one of the battery cables and cranking right? i am asking could i have found this problem to.

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